1. Field of the Invention
The present invention relates to an electron beam apparatus and an image forming apparatus such as a display device as an application of such an electron beam apparatus. More particularly, the present invention relates to an electron beam apparatus and an image forming apparatus having atmospheric pressure withstanding structure, and a method of manufacturing thereof.
2. Related Background Art
Two kinds of devices, i.e., a thermoionic cathode device and a cold cathode device are conventionally known as electron-emitting devices. Known cold cathode devices include a surface conduction electron-emitting device, a field emission type device (hereinafter referred to as “FE type”), a metal/insulating layer/metal type emitting device (hereinafter referred to as ““MIM type”).
As a surface conduction electron-emitting device, one disclosed in, for example, M. I. Elinson, Radio Eng. Electron Phys., 10, 1290 (1965) and others as will be described in the following are known.
A surface conduction electron-emitting device utilizes the phenomenon in which electron emission is caused by flowing electric current to a thin film formed on a substrate and having a small area so as to be in parallel to the film surface. The surface conduction electron-emitting device that has been reported includes those employing an SnO2 thin film developed by Elinson et al. referred to above, those employing an Au thin film (G. Dittmer: “Thin Solid Films”, 9, 317 (1972), those employing an In2O3/SnO2 thin film (M. Hartwell and C. G. Fonstad: “IEEE Trans. ED Conf.”, 519 (1975), and those employing a carbon thin film (Hisashi Araki, et al. “Shinku (Vacuum)”, Vol. 26, No. 1, 22 (1983).
A typical device structure example of these surface conduction electron-emitting devices is shown in FIG. 26, which is a plan view of a device disclosed by M. Hartwell et al. referred to above. In the figure, reference numeral 3001 denotes a substrate, and reference numeral 3004 denotes a conductive thin film made of metal oxide formed by sputtering. The conductive thin film 3004 is formed to be H-shaped in plan view as illustrated. The conductive thin film 3004 is subjected to energization operation called energization forming, as will be described later, to form an electron-emitting region 3005. Intervals L and W in the figure are defined as 0.5 mm to 1 mm and 0.1 mm, respectively. For convenience of illustration, the electron-emitting region 3005 is shown as a rectangle formed in the middle of the conductive thin film 3004, but it is only a schematic illustration and the exact position and shape of the actual electron-emitting region are not faithfully expressed herein.
In the above-mentioned surface conduction electron-emitting device represented by the devices disclosed in M. Hartwell et al, it has been typically practiced to form the electron-emitting region 3005 by an energization operation called energization forming on the conductive thin film 3004 before effecting the electron emission. More specifically, in energization forming, constant dc voltage or dc voltage increasing at a very slow rate, for example, on the order of 1 v/minute, is applied to both ends of the conductive thin film 3004 for energization to locally destroy, deform, or denature the conductive thin film 3004, thus forming the electron-emitting region 3005 kept in a state of high electrical resistance. It is to be noted that a fissure is formed in a portion of the conductive thin film 3004, which is locally destroyed, deformed, or denatured. If appropriate voltage is applied to the conductive thin film 3004 after the energization forming, electron emission is carried out in the vicinity of the fissure.
Known examples of the FE type are disclosed in, for example, W. P. Dyke & W. W. Dolan, “Field emission”, Advance in Electron Physics, 8, 89 (1956), C. A. Spindt, “Physical properties of thin-film field emission cathodes with molybdenum cones”, J. Appl. Phys., 47, 5248 (1976), etc.
A typical device structure example of the FE type is shown in FIG. 27, which is a sectional view of a device disclosed by C. A. Spindt et al. referred above. In the figure, reference numeral 3010 denotes a substrate, reference numeral 3011 denotes emitter wiring, reference numeral 3012 denotes an emitter cone, reference numeral 3013 denotes an insulating layer, and reference numeral 3014 denotes a gate electrode. In the device, by applying the appropriate voltage between the emitter cone 3012 and the gate electrode 3014, an electric field emission from the tip of the emitter cone 3012 is caused.
As another device structure example of the FE type, different from the laminated structure shown in FIG. 27, there is also a case where an emitter and a gate electrode are disposed on a substrate substantially in parallel with the substrate plane.
Known examples of the MIM type are disclosed in, for example, C. A. Mead, “Operation of tunnel-emission Devices”, J. Appl. Phys., 32, 646 (1961). A typical device structure example of the MIM type is shown in a sectional view of FIG. 28. In the figure, reference numeral 3020 denotes a substrate, reference numeral 3021 denotes a lower electrode made of metal, reference numeral 3022 denotes a thin insulating layer with the thickness of about 100 Å. Reference numeral 3023 denotes an upper electrode made of metal with the thickness of about 80 to 300 Å. In the MIM type, by applying the appropriate voltage between the upper electrode 3023 and the lower electrode 3021, an electron emission from the surface of the upper electrode 3023 is caused.
With regard to the cold cathode devices mentioned above, since electron emission can be caused at a lower temperature than the case of a thermoionic cathode device, a heater for heating is not necessary. This makes the structure simpler than that of a thermoionic cathode device, and a minute device can be formed. Further, even if a large number of devices are densely disposed, problems such as thermal melting of the substrate are less liable to occur. Further, different from the case of a thermoionic cathode device in which the response speed is low because the device operates by heating with a heater, the cold cathode device has an advantage in that the response speed is high. This leads to the active research for applying the cold cathode devices.
For example, the surface conduction electron-emitting device has an advantage in that, since it is particularly simple in structure and easily manufactured among the cold cathode devices, a large number of the surface conduction electron-emitting devices can be formed over a large area. Therefore, methods of arranging and driving a large number of such devices have been studied as disclosed by the present applicant in Japanese Patent Application Laid-open No. Sho 64-31332.
Applications of the surface conduction electron-emitting device that has been studied include an image forming apparatus such as an image display device and an image recording device, and a charging beam source. In particular, an application to the image display device that has been studied includes an image display device using a surface conduction electron-emitting device in combination with a phosphor, which emits light by being irradiated by electron beams, as disclosed by the present applicant in U.S. Pat. No. 5,066,883 and Japanese Patent Application Laid-open Nos. Hei 2-257551 and Hei 4-28137. The image display device using the combination of a surface conduction electron-emitting device and a phosphor is expected to achieve more excellent characteristics than other conventional image display devices. For example, it can be said that such an image display device is superior to a liquid crystal display device, which has been recently popularized, in that no back light is necessary because it is of a self-emission type and in that it has a larger angle of visibility.
A method of driving a large number of the FE type devices disposed is disclosed, for example, by the present applicant in U.S. Pat. No. 4,904,895. A known example of an application of the FE type to an image display device is a plane-type display device reported by R. Meyer et al. (R. Meyer: “Recent Development on Microtips Display at LETI”, Tech. Digest of 4th Int. Vacuum Microelectronics Conf., Nagahama, pp. 6–9 (1991)).
An example of applying a large number of the disposed MIM-type devices to an image display device is disclosed, for example, in Japanese Patent Application Laid-open No. Hei 3-55738.
Among the image forming apparatus using electron-emitting devices described above, attention is being paid to a plane-type display device as a device to replace a cathode ray tube type display device, since it saves space and it is lightweight.
FIG. 29 is a perspective view of an example of a display panel portion of a plane-type image display device, with a part of the panel cut away to reveal the internal structure.
In the figure, reference numeral 3115 denotes a rear plate, reference numeral 3116 denotes side walls, and reference numeral 3117 denotes a face plate. The rear plate 3115, the side walls 3116, and the face plate 3117 form an envelope (airtight container) for maintaining the vacuum inside the display panel. A substrate 3111, which is fixed to the rear plate 3115, has n×m cold cathode devices 3112 formed thereon (n and m are positive integers, which are 2 or above, and are appropriately selected according to the target number of the display pixels). As shown in FIG. 29, the n×m cold cathode devices 3112 are wired by m wirings 3113 in the row direction and n wirings 3114 in the column direction. The portion formed of the substrate 3111, the cold cathode devices 3112, the row direction wirings 3113, and the column direction wirings 3114 is referred to as a multiple electron beam source. An insulating layer (not shown) between the row direction wirings 3113 and the column direction wirings 3114 is formed at least at the intersections of the two wirings to maintain electric insulation.
A fluorescent film 3118 formed of phosphors is formed on the underside of the face plate 3117 where phosphors (not shown) are individually colored into the three primary colors, i.e., red (R), green (G), and blue (B). Black portions (not shown) are provided between the respective phosphors in the three colors forming the fluorescent film 3118. Further, a metal back 3119 of Al or the like is formed on the surface of the fluorescent film 3118 on the side of the rear plate 3115.
Dx1 to Dxm, Dy1 to Dyn, and Hv are airtight electric connection terminals provided for an electric connection between the display panel and an electric circuit, which is not shown. Dx1 to Dxm are electrically connected with the row direction wirings 3113 of the multiple electron beam source, Dy1 to Dyn are electrically connected with the column direction wirings 3114 of the multiple electron beam source, and Hv is electrically connected with the metal back 3119.
The inside of the airtight container is kept at a vacuum of about 110 Pa. As the display area of the image display device becomes large, a means for preventing deformation or breakage of the rear plate 3115 and the face plate 3117, due to the air pressure difference between the inside of the airtight container and the outside, becomes more necessary. A method to do this by thickening the rear plate 3115 and the face plate 3116 not only increases the weight of the image display device, but also causes distortion and parallax of an image when viewed from an oblique angle. On the other hand, in FIG. 29, structural supports (referred to as spacers or ribs) 3120 formed of relatively thin glass plates for supporting the atmospheric pressure are provided. In this way, the distance between the substrate 3111 with the multiple electron beam source formed thereon and the face plate 3117 with the fluorescent film 3118 formed thereon is typically kept on a sub-millimeter level or is only several millimeters, with the inside of the airtight container being kept at a high vacuum as described above.
In the image display device using a display panel described above, when voltage is applied to the respective cold cathode devices 3112 through the terminals Dx1 to Dxm and Dy1 to Dyn outside the container, the respective cold cathode devices 3112 emit electrons. At the same time, high voltage of several hundred V to several kV is applied to the metal back 3119 through the terminal Hv outside the container to accelerate the emitted electrons and have them impact the inner surface of the face plate 3117. This excites the phosphors in the three colors forming the fluorescent film 3118 to emit light and display an image.